The effects of maternal magnesium sulfate treatment on newborns: a prospective controlled study.

OBJECTIVE: To evaluate the effects of maternal magnesium sulfate treatment on newborn outcome.
METHODS: Subjects were newborn infants delivered at > or = 34 weeks of gestation whose mothers received a minimum of 12 hours of intravenous MgSO4 therapy before delivery. Control infants were the next born infants of similar gestational age. Outcome recorded at delivery included Apgar scores, whether resuscitation was required, and whether respiratory depression or decreased tone were noted by the physician in attendance. Pneumocardiograms on magnesium-exposed and control infants, obtained within 6 to 18 hours after delivery, were analyzed postdischarge by a single investigator who was blinded to group. The nursery course, feeding patterns, time to first stool, and time to first void were recorded. All patient care decisions, including admission to the neonatal intensive care unit (NICU) or term nursery, were independent of study protocol.
RESULTS: A total of 26 magnesium-exposed and 26 control infants were enrolled. The mean total dose of MgSO4 before delivery was 51.2+/-24 gm; the mean duration of therapy was 23.1+/-10 hours. The mean maternal serum magnesium level before delivery was 5.8+/-1.1 mg/dl. The infants' mean cord or initial serum magnesium level was 5.2+/-1.0 mg/dl, which correlated with the maternal magnesium level before delivery (r=0.81, p < 0.001). MgSO4-exposed infants had a higher incidence of hypotonia and lower median Apgar scores than control infants (p < 0.001). However, there was no association between adverse outcomes and maternal serum magnesium concentrations at delivery, duration of treatment, or dose of MgSO4. No difference in dose or length of maternal MgSO4 treatment was noted between infants admitted to term nursery and those admitted to NICU. Pneumocardiogram data were similar between MgSO4-exposed and control infants (all p > or = 0.16). There were no significant differences in number of episodes of feeding intolerance or in time to first stool or void between MgSO4-exposed and control infants (all p > or = 0.31).
CONCLUSION: Infants born to mothers treated with MgSO4 were more likely to be hypotonic and have lower Apgar scores at birth. Beyond the immediate postdelivery period, there were no additional complications in this cohort attributable to prenatal MgSO4 exposure. We suggest that pediatricians attend deliveries of magnesium-exposed infants.